The present disclosure relates to a MEMS device such as a sensor utilizing a MEMS (Micro Electro Mechanical Systems) technique, and relates to, e.g., an acoustic sensor which has a diaphragm vibrating by detecting a pressure variation, and which converts such vibration into an electrical signal.
Recently, a technology called “MEMS” has been developed by utilizing microfabrication techniques used in a field of fabricating semiconductor LSIs such as silicon. Various micro-components such as acceleration sensors, pressure sensors, and acoustic sensors have been proposed and commercialized by utilizing the MEMS technique.
As disclosed in, e.g., Patent Documents 1 and 2, these MEMS devices such as sensors utilizing the MEMS technique includes a structure which has a diaphragm to be a vibrating region (hereinafter referred to as a “diaphragm structure”) in order to detect an acceleration or pressure variation.
A diaphragm structure in a conventional MEMS device will be explained hereinafter with reference to FIGS. 3(a)-3(c). FIG. 3(a) is a top view of the diaphragm structure in the conventional MEMS device. FIG. 3(b) is a cross-sectional view of the diaphragm structure in the conventional MEMS device. FIG. 3(c) is a bottom view of the diaphragm structure in the conventional MEMS device.
As shown in FIG. 3(a)-3(c), the diaphragm structure in the conventional MEMS device is a structure in which a thin film 303 is formed on a substrate 301 having a through-hole 302, and a portion of the thin film 303, which is positioned on the through-hole 302, functions as a diaphragm 304. The diaphragm 304 vibrates depending on an acceleration or pressure variation, and thereby utilizing the diaphragm 304 for MEMS devices such as various sensors by electrically detecting such vibration displacement.
As the substrate 301, a silicon substrate is generally used, but a (100) plane oriented silicon substrate is particularly used. A mask film is patterned and formed onto the (100) plane oriented silicon substrate, and is etched with alkali such as KOH. While etching the (100) plane, a (111) plane which has an etching rate 50-100 times slower than that of the (100) plane is exposed. Hence, an anisotropic wet etching can be performed with a good dimensional controllability. As shown in FIGS. 3(a) and 3(c), when continuing the etching until the through-hole 302 penetrates the silicon substrate 301, the square diaphragm 304 is formed. As inner walls of the through-hole 302, (111) inclined surfaces 305 having an angle of 54.7 degrees with respect to the (100) plane.
Patent Document 2 discloses a square diaphragm formed by using a (110) plane oriented silicon substrate instead of using the (100) plane oriented silicon substrate.
PATENT DOCUMENT 1: Japanese Patent Publication No. 60-138434
PATENT DOCUMENT 2: Japanese Patent Publication No. 2002-223499
PATENT DOCUMENT 3: Japanese Patent Publication No. 2007-67659